Zoom lens systems provided with an anti-vibration function are disclosed in Japanese Laid-Open Patent Application Nos. 6-337375 and 6-123836. In a zoom lens system consisting of five or more lens groups, these systems have the second lens group, third lens group, etc. intersect the optical axis and vary their positions to prevent vibration.
Nevertheless, each of the zoom lens systems described in the aforesaid publications is primarily a telephoto zoom lens system, and the field of view at the wide-angle end is smaller than 30 degrees. Furthermore, the effective F number is large-about F/4-F/5.6-so that under bright conditions the picture goes black and this is not sufficient for photographing dark subjects. Instead of this, what has long been needed is a large-aperture, wide-angle, high-zoom ratio, high-performance, anti-vibration optical system for a zoom lens.
Also, optical systems utilized for electronic imaging devices and so forth often position optical low-pass filters or three-color separation filters, mirrors, etc. behind the lens, so that a sufficiently large back focus is also required.
It is also necessary to provide sufficient peripheral illumination at the periphery of the image plane in order to minimize shading, and to maintain sufficient telecentricity at the image side.